This invention relates generally to gas turbine engines, and more specifically to rotor shafts used with gas turbine engines.
At least some known gas turbine engines include a core engine having, in serial flow arrangement, a fan assembly, a high pressure compressor which compress airflow entering the engine, a combustor which burns a mixture of fuel and air, and low and high pressure turbines which each include a plurality of rotor blades that extract rotational energy from airflow exiting the combustor. The fan assembly and the low pressure turbine are coupled by a first shaft, and the high pressure compressor and the high pressure turbine are coupled by a second shaft.
During engine operation, the fan assembly and the low-pressure turbine are subjected to different operating temperatures, pressures, and stresses than those that the high pressure turbine and compressor are subjected. As a result, within at least some known gas turbine engines, the rotor shaft coupling the low pressure components is fabricated from a different material than the heavier, more durable material used in fabricating the rotor shaft that couples the high pressure components. However, because the low-pressure shaft extends the length of the gas turbine engine, a portion of the low-pressure shaft is exposed to the same temperatures and pressures as the high pressure turbine components. To facilitate optimizing engine weight considerations with operating stresses that may be induced to the shaft, at least some known low-pressure shafts include an upstream portion that is fabricated form a first material and a downstream portion that is fabricated from a second material. For example, a forward portion of the low-pressure shaft connected to the fan assembly and the aft portion of the low-pressure shaft connected to the low-pressure turbine may be fabricated from a nickel alloy, while an intermediate portion of the shaft extending through the compressor and high pressure turbine may be fabricated from a titanium alloy. Because such materials are dissimilar, explosive bonding is used to create a bonded joint that is then used to couple the two nickel shaft portions to the intermediate titanium alloy section of the shaft such that the bonded joint extends therebetween.
A low strength inner layer material is used to separate the plates used in forming the bonded joint. The inner layer material facilitates preventing the production of deleterious intermetallic compounds across the bonded joint. More specifically, the low strength inner layer material extends diametrically across the bonded joint, such that when the rotor shaft portions are coupled at the bonded joint, the inner layer of material extends substantially perpendicularly to a centerline axis of symmetry of the shaft. Within known bond joints, when the shaft is rotated, the low strength material resides completely in a plane of maximum shear stress. As a result, during engine operation, the inner layer material may significantly limit the performance of the bonded joint.
In one aspect of the invention, a method for manufacturing a rotor shaft is provided. The method comprises fabricating a first shaft portion that extends axially from a first end to a second end, fabricating a second shaft portion that extends axially from a first end to a second end, and coupling the second shaft portion to the first shaft portion with an explosive bonded joint such that the second shaft portion is aligned substantially concentrically with respect to the first shaft portion, and such that the bonded joint extends obliquely with respect to a centerline axis of symmetry of the rotor shaft.
In another aspect, a rotor shaft is provided. The rotor shaft includes a first shaft portion that extends axially from a first end to a second end, and a second portion that extends axially from a first end to a second end, wherein the first shaft portion is coupled to the second portion at a bonded joint such that the first shaft portion is substantially axially-aligned with respect to the second shaft portion. The bonded joint extends obliquely with respect to a centerline axis of symmetry of the rotor shaft.
In a further aspect of the invention, a gas turbine rotor shaft is provided. The gas turbine rotor shaft includes a first shaft portion, a second shaft portion, and a bonded joint extending therebetween. The bonded joint is substantially concentrically aligned with respect to said first and second portions, and is oblique with respect to a centerline axis of symmetry extending axially through the rotor shaft.